STL Science Center

STL Science Center

26 September 2012

Arrhinoceratops and That Unique Nose

Taken from Paleopedia
Arrhinoceratops has a rather interesting nose horn. There is no debate about whether its nose horn was a shielded boss like Pachyrhinosaurus or if it was actually a Triceratops-like horn which eventually sloped upward. The nasal horn of Arrhinoceratops was originally described as not existing and instead interpreted the small bone on which the horn's keratin sheath would have developed simply as a deformity of the skull due to compression during fossilization. The horn is indeed small and it barely angles upward; in fact, the bony core of horn actually juts nearly directly forward off the sloping nasal bone. Arrhinoceratops has been cited as possessing evidence that the nasal horn core is a separate ossification from the nasal bone, though it has been doubted that this is true.  The nasal itself is somewhat thin with, as in all Chasmosaurine skulls, an extremely large pair of nares (hole for the sinus and olfactory organs). The frill of Arrhinoceratops is also very typical for Chasmosaurs and is of a moderate length, about in the average size range for a moderate to larger Chasmosaur. Chasmosaurs as a group are the largest, as well as the youngest, group of Ceratopsians and therefore, even without any postcranial skeletal elements to go by, it can be safely assumed that Arrhinoceratops would have been a rather large animal. Estimates of size based on skull to body ratios of other Chasmosaurs and the skull of Arrhinoceratops place the animal at approximately 6m (20ft).

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